CN113070083B - A kind of high-efficiency catalytic oxidation propane catalyst and preparation method thereof - Google Patents

Abstract

The invention discloses a high-efficiency catalytic oxidation propane catalyst and a preparation method thereof. The catalyst prepared by the method has a large specific surface area and abundant oxygen vacancies. The technical scheme is as follows: First, Co(NO ₃ ) ₂ ·6H ₂ O, Al(NO ₃ ) ₃ ·6H ₂ O and urea are used as raw materials to prepare CoAl hydrotalcite-derived composite oxide precursor, and then calcined in air to obtain CoAl Hydrotalcite-derived composite oxide; finally calcined in NH ₃ to obtain the target product N-CoAlO in sheet form. The results show that by a simple NH ₃ treatment method, N is incorporated into it, and part of the Co ³⁺ is converted into Co ²⁺ , thereby successfully introducing more oxygen vacancies and forming a catalyst with higher catalytic oxidation activity of propane. The preparation process is simple, the operability is strong, and the cost is low.

Description

A kind of high-efficiency catalytic oxidation propane catalyst and preparation method thereof

technical field

The invention relates to a preparation method of a sheet-like CoAl composite oxide, in particular to an N-doped catalyst with high catalytic activity for propane.

Background technique

Volatile organic compounds (VOCs) emitted from industrial production processes and vehicle exhaust not only pollute the atmosphere, but also endanger human health. Propane is a component of VOCs in the atmosphere, and its stable molecular structure is difficult to destroy. Therefore, the elimination of propane is one of the urgent problems to be solved. Noble metal catalysts show high activity for the deep oxidation of propane at lower temperatures, but their high cost and easy sintering greatly limit their industrial applications. _{Co3O4 possesses} mixed cation valence states, abundant reactive oxygen species and redox properties, but limited surface oxygen availability hinders its catalytic oxidation activity. Studies have shown that increasing the content of Co ²⁺ or by N doping can introduce oxygen vacancies on Co ₃ O ₄ , which is very effective to enhance the migration and reaction of active oxygen on its surface. A simple NH ₃ reduction treatment can achieve the above two goals at the same time, when there is a pain point in this method, that is, the Co ₃ O ₄ after being reduced by NH ₃ is unstable and easily oxidized in the air.

CoAl hydrotalcite-derived composite oxides have many advantages, such as good dispersibility, large specific surface area and good thermal stability. In order to solve this problem, the present invention firstly prepared CoAl hydrotalcite-derived composite oxide by hydrothermal method, and then treated with NH to prepare sheet _- like N-doped CoAl hydrotalcite-derived composite oxide. The doped CoAl hydrotalcite-derived composite oxide exhibits efficient catalytic oxidation performance of propane.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a sheet-like N-doped CoAl hydrotalcite-derived composite oxide catalyst and a preparation method thereof.

To achieve the above object, the present invention adopts the following technical solutions:

In the present invention, the flaky N-doped CoAl hydrotalcite-derived composite oxide is prepared by a combination of a hydrothermal method and an NH ₃ treatment method. The specific steps are as follows:

1) Weigh Co(NO ₃ ) ₂ ·6H ₂ O and Al(NO ₃ ) ₃ ·6H ₂ O, add them into deionized water and stir to dissolve, then add urea, and stir quickly until dissolved;

2) Transfer the mixed solution obtained in step 1) to a 100 mL hydrothermal kettle, and place it in a 150 ^o C oven for 6 hours;

3) filter the precipitate obtained in step 2), wash with deionized water, and then place the precipitate in an oven to dry to obtain a CoAl hydrotalcite-derived composite oxide precursor;

4) The pink CoAl hydrotalcite-derived composite oxide precursor obtained in step 3) is placed in a muffle furnace and calcined at a constant temperature of 400ºC for 4 hours, to obtain a CoAl hydrotalcite-derived composite oxide.

5) The CoAl hydrotalcite-derived composite oxide obtained in step 4) is calcined at a constant temperature of 400 ^o C in a 5 vol % NH ₃ /Ar atmosphere.

In the above step 1), the material ratio of the Co(NO ₃ ) ₂ ·6H ₂ O to Al(NO ₃ ) ₃ ·6H ₂ O is 3:1-3.

In the above step 4), the calcination heating rate of the pink sample is 2-10 ^o C/min.

In the above step 5), the duration of constant temperature calcination of the CoAl hydrotalcite-derived composite oxide is 2 h, 4 h and 6 h, respectively.

The above-mentioned method can be used to prepare the flaky N-doped CoAl hydrotalcite-derived composite oxide for the efficient catalytic oxidation of propane.

As can be seen from the above technical solutions, the significant advantages of the present invention are:

1) The NH ₃ treatment method used in the present invention can reduce a part of Co ₃ O ₄ to CoO, and generate more Co ²⁺ while retaining as much Co ³⁺ as possible. On the other hand, the _NH3 treatment method doped as much N into the CoAl hydrotalcite-derived composite oxide as possible. Both aspects contribute to the generation of oxygen vacancies and improve the oxygen mobility of CoAlO, thereby enhancing the catalytic oxidation performance for propane.

2) The present invention uses CoAl hydrotalcite-derived composite oxide as the NH ₃ treatment object, which can not only smoothly dope N into the Co-based oxide, but also overcome the instability of Co ₃ O ₄ after NH ₃ treatment, and it is easily affected by The problem of air oxidation.

3) The N-CoAlO prepared by the present invention has efficient catalytic oxidation performance and good stability. For example, under the test conditions of C ₃ H ₈ =8000 ppm, space velocity = 12000 mL h ^-1 g ^-1 , the propane degradation rate of N-CoAlO/4h at 266 ^o C can reach 90%; after 5 cycles of performance tests After that, the propane degradation rate of N-CoAlO/4h hardly changed.

Description of drawings

FIG. 1 is an XRD pattern of the N-doped CoAl hydrotalcite-derived composite oxide obtained in Example 1. FIG.

Figure 2 is the SEM image of the product obtained in Example 1; in the figure: (a), (b) SEM images of CoAlO LDHs, (c), (d) SEM images of CoAlO, (e), (f) N-CoAlO SEM images of /4h, (g), (h) SEM images of N-CoAlO/4h- after cycling test.

Figure 3 is a TEM image of the product obtained in Example 1, in which: (a), (d) TEM images of CoAlO LDHs, (b), (e) TEM images of CoAlO, (c), (f) N-CoAlO TEM image of /4h.

4 is a graph showing the performance curve of propane catalytic oxidation of the N-doped CoAl hydrotalcite-derived composite oxide obtained in Example 1 under the test conditions of C ₃ H ₈ = 8000 ppm, space velocity = 12000 mL h ⁻¹ g ⁻¹ .

5 is a cycle test performance diagram of the N-CoAlO/4h catalyst obtained in Example 1 under the test conditions of C ₃ H ₈ = 8000 ppm, space velocity = 12000 mL h ⁻¹ g ⁻¹ .

Detailed ways

Example 1

1) Weigh 4.3655 g of Co(NO ₃ ) ₂ ·6H ₂ O and 1.8757 g of Al(NO ₃ ) ₃ ·6H ₂ O, dissolve them in 75 mL of deionized water at room temperature with magnetic stirring, and add 3.003 g of The urea was added to the above mixed solution, stirred and dissolved;

2) Transfer the mixed solution obtained in step 1) into a 100 mL hydrothermal kettle, and place it in a 150 ^o C oven for 6 h;

3) Filter the precipitate obtained in step 2), wash it with deionized water at least 5 times, and then place the precipitate in an oven at 80 ^o C and dry for 12 h to obtain the CoAl hydrotalcite-derived composite oxide precursor (denoted as CoAlO LDHs). );

4) Then, the pink CoAl hydrotalcite-derived composite oxide precursor obtained in step 3) was placed in a crucible, and was calcined at a constant temperature of 400 ºC in a muffle furnace at a heating rate of 2 ºC/min for 4 ^h , that is, A CoAl hydrotalcite-derived composite oxide (referred to as CoAlO) was obtained.

5) The CoAlO synthesized in step 4) was calcined at 400 ^o C in a 5 vol % NH ₃ /Ar atmosphere for 2 h, 4 h and 6 h respectively (denoted as N-CoAlO/2h, N-CoAlO, respectively). /4h and N-CoAlO/6h).

Figure 1 shows the XRD pattern of N-doped CoAl hydrotalcite-derived composite oxides. It can be seen from Figure 1 that the diffraction peak positions of CoAlO after calcination in air at 400 ^o C are related to the standard spectrum of Co ₃ O ₄ (JCPDS, 65- 3103) to match. The corresponding crystal plane indices are shown in Figure 1. When CoAlO was calcined in _NH3 atmosphere for 2 h, part of Co3O4 was reduced to CoO _; when _NH3 treatment time reached ₄ h, the sample showed stronger CoO diffraction peak at 2θ = ^61.7o , indicating that there were more Co ₃ O ₄ was reduced to CoO; when the NH ₃ treatment time was extended to 6 hours, no obvious Co ₃ O ₄ diffraction peak was observed, indicating that most of the Co ₃ O ₄ was reduced to CoO. The above results show that NH ₃ treatment with different durations has a great influence on the phase of CoAlO.

Figure 2 shows the SEM images of the resulting CoAlO LDHs, CoAlO and N-CoAlO/4h. It can be seen from (a) and (b) in Fig. 2 that CoAlO LDHs are hexagonal flakes; from (c)-(f) in Fig. 2, it can be seen that CoAlO and N-CoAlO/4h exhibit the same properties as CoAlO LDHs. Hexagonal flakes, indicating that _NH3 treatment has no obvious effect on the morphology of CoAlO. To investigate the thermal stability of N-CoAlO/4h, the morphology of N-CoAlO/4h after cycling tests was observed. It can be seen from (g) and (h) in Fig. 2 that N-CoAlO/4h still maintains a relatively complete shape after the cycling test, indicating that N-CoAlO/4h has good thermal stability.

Figure 3 shows the TEM images of the resulting CoAlO LDHs, CoAlO and N-CoAlO/4h. The CoAlO LDHs, CoAlO and N-CoAlO/4h exhibit hexagonal flakes as further evidenced by (a)–(c) of Fig. 3. Meanwhile, the lattice fringes of N-CoAlO/4h correspond to the interplanar spacings of 0.24 and 0.21 nm, which are consistent with the d ₃₁₁ and d ₂₀₀ spacings in the XRD patterns of Co ₃ O ₄ and CoO, proving that Co ₃ O ₄ and CoO also exists in N-CoAlO/4h.

FIG. 4 is a graph showing the catalytic oxidation activity of N-doped CoAl hydrotalcite-derived composite oxide for propane. It can be seen from Fig. 4 that N-CoAlO/4h exhibits the best catalytic oxidation performance of propane, which indicates that NH ₃ treatment for an appropriate duration can improve the catalytic oxidation performance of CoAlO for propane.

Figure 5 is a test chart of the cycle performance of N-CoAlO/4h for catalytic propane oxidation. It can be seen from Figure 5 that the catalytic oxidation performance of N-CoAlO/4h to propane has almost no decrease after 5 cycles of performance tests, indicating that N-CoAlO/4h has good stability.

Example 2 (different amounts of Co(NO ₃ ) ₂ ·6H ₂ O)

1) Weigh 1.4552 g of Co(NO ₃ ) ₂ ·6H ₂ O and 1.8757 g of Al(NO ₃ ) ₃ ·6H ₂ O, dissolve them in 75 mL of deionized water at room temperature with magnetic stirring, and add 3.003 g of The urea was added to the above mixed solution, stirred and dissolved;

2) Transfer the mixed solution obtained in step 1) into a 100 mL hydrothermal kettle, and place it in a 150 ^o C oven for 6 h;

3) Filter the precipitate obtained in step 2), wash it with deionized water at least 5 times, and then place the precipitate in an oven at 80 ^o C and dry for 12 h to obtain the CoAl hydrotalcite-derived composite oxide precursor;

4) Then the pink CoAl hydrotalcite-derived composite oxide precursor sample obtained in step 3) was placed in a crucible, and was calcined at a constant temperature of 400 ºC in a muffle furnace at a heating rate of 2 ºC/min for 4 ^hours . That is, the CoAl hydrotalcite-derived composite oxide is obtained.

5) The CoAlO synthesized in step 4) was calcined in a 5 vol % NH ₃ /Ar atmosphere at 400 ^o C for 2 h, 4 h and 6 h.

Example 3 (different calcination heating rate)

1) Weigh 4.3655 g of Co(NO ₃ ) ₂ ·6H ₂ O and 1.8757 g of Al(NO ₃ ) ₃ ·6H ₂ O, dissolve them in 75 mL of deionized water at room temperature with magnetic stirring, and add 3.003 g of The urea was added to the above mixed solution, stirred and dissolved;

2) Transfer the mixed solution obtained in step 1) into a 100 mL hydrothermal kettle, and place it in a 150 ^o C oven for 6 h;

3) Filter the precipitate obtained in step 2), wash it with deionized water at least 5 times, and then place the precipitate in an oven at 80 ^o C and dry for 12 h to obtain the CoAl hydrotalcite-derived composite oxide precursor;

4) Then the pink CoAl hydrotalcite-derived composite oxide precursor sample obtained in step 3) was placed in a crucible, and was calcined at a constant temperature of 400 ºC in a muffle furnace at a heating rate of 10 ºC/min for 4 ^hours . That is, the CoAl hydrotalcite-derived composite oxide is obtained.

5) The CoAlO synthesized in step 4) was calcined in a 5 vol % NH ₃ /Ar atmosphere at 400 ^o C for 2 h, 4 h and 6 h.

The above descriptions are only preferred embodiments of the present invention, and all equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope of the present invention.

Claims (5)

1. a simple preparation method for the sheet-like N-doped CoAl composite oxide of propane efficient catalytic oxidation, is characterized in that, comprises the steps: 1) Weigh Co(NO ₃ ) ₂ 6H ₂ O and Al(NO ₃ ) ₃ 6H ₂ O, add them to deionized water, stir to dissolve, then add urea, and stir rapidly until dissolved to obtain a mixed solution; 2) Transfer the mixed solution obtained in step 1) to a 100 mL hydrothermal kettle, and place it in a 150 ^o C oven for 6 hours to obtain a precipitate; 3) filter the precipitate obtained in step 2), wash with deionized water, and then place the precipitate in an oven to dry to obtain a CoAl hydrotalcite-derived composite oxide precursor; 4) The CoAl hydrotalcite-derived composite oxide precursor obtained in step 3) is placed in a muffle furnace and calcined at a temperature of 400 ºC, and calcined at a constant temperature of 400 ºC for 4 hours, to obtain a CoAl hydrotalcite-derived composite oxide; 5) The CoAl hydrotalcite-derived composite oxide obtained in step 4) is calcined at a constant temperature of 400 ^o C in a 5 vol % NH ₃ /Ar atmosphere to obtain a sheet-like N-doped CoAl composite oxide. 2. a kind of simple preparation according to claim 1 is to the method for the sheet N-doped CoAl composite oxide of propane efficient catalytic oxidation, it is characterized in that In step 1), the material ratio of the Co(NO ₃ ) ₂ ·6H ₂ O to Al(NO ₃ ) ₃ ·6H ₂ O is 3:1-3. 3. a kind of simple preparation method according to claim 1 and 2 to the sheet N-doped CoAl composite oxide of propane efficient catalytic oxidation, is characterized in that In step 4), the heating rate of the heating and calcining of the CoAl hydrotalcite-derived composite oxide precursor is 2-10 ^o C/min. 4. a kind of simple preparation method according to claim 1 to the sheet-like N-doped CoAl composite oxide of propane efficient catalytic oxidation, is characterized in that In step 5), the duration of constant temperature calcination of the CoAl hydrotalcite-derived composite oxide is 2 h, 4 h or 6 h, respectively. 5. A sheet-like N-doped CoAl composite oxide catalyst is prepared by the method of any one of claims 1-4.

Images